1. Field of the Invention
The invention relates to constant current source devices, especially to CMOS constant current source devices.
2. Brief Description of the Prior Art
A number of integrated circuit decoder driver circuits are available for driving a number of light-emitting diode (LED) devices. For example, the Motorola MC14511 BCD-to-seven segment latch/decoder/driver circuit constructed with CMOS technology is such a device. However, the means for controlling the amount of output current supplied to each LED must be controlled by use of external resistors connected in series with the LED. The requirement for a separate external series resistor to control the brightness of each LED is expensive and inconvenient. Further, the output current delivered by the drivers of the known decoder driver circuits tends to be quite dependent on the integrated circuit manufacturing process parameters, which vary more than is desirable.